The present invention concerns an equipment for respiratory protection against pollutants and noxious products, for use at low altitude (typically up to 12,500 ft) that is to say, in an atmosphere whose pressure is sufficiently high for rendering unnecessary to supply oxygen-enriched air to the lungs. It finds a particularly important application in so-called NBC protective equipment, designed to protect at least the respiratory tract (and often the entire skin surface) of a wearer against pollutants dispersed in the atmosphere.
Equipment of this type is already known, comprising a face cover (hood or full mask if the entire head must be protected, mask covering the breathing orifices if skin protection is unnecessary or is achieved by other means) fitted with an atmospheric air supply comprising a filter, a rotary fan or blower to compensate for the head loss due to the filter, and a flexible hose, as well as a self-contained electric power source for the rotary fan, supplying a rated voltage V.sub.0 to the motor of the fan.
The air flow to be supplied to the wearer of the equipment changes enormously depending on the degree of activity of the wearer. It is generally in conditions in which protection is indispensable that the wearer requires a maximum flow rate, either during a single unhale period, or during a significant time interval. In fact, an air draw by inspiration which is not immediately offset by an available delivery air flow rate causes the face mask to be under negative pressure and a risk of ingress of polluted air.
The problem can be alleviated by connecting a flexible economizer bag to the face cover. While this solution helps to absorb short inspiratory peaks, it does not make it possible to offset increases in the average flow rate. Moreover, economizer bags are bulky and prone to wear and tear.
In consequence, the solution generally adopted so far has been to dimension the fan so that it continuously supplies a flow rate at least equal to the needs in the most critical conditions. However, this increases electric power consumption and hence necessitates an increase in weight of the batteries for a given operational life. The large air flow rate which permanently passes through the filter reduces its service life unnecessarily due to faster clogging.
A breathing apparatus is also known (EP-A-0334555) having an outer full face mask and an inner oro-nasal mask. Means responsive to the pressure difference across the oro-nasal mask disable the fan at the commencement of each inhale period and energize the fan at the commencement of each unhale period. Such an apparatus is complex; the fan operates under conditions which may detrimentally affect its life. The buffer space between the masks increases the head loss.